[libcxx-commits] [libcxx] [libc++] Fix UB in bitwise logic of {std, ranges}::{fill, fill_n} algorithms (PR #122410)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_SUPPORT_SIZED_ALLOCATOR_H
+#define TEST_SUPPORT_SIZED_ALLOCATOR_H
+
+#include <cstddef>
+#include <limits>
+#include <memory>
+#include <new>
+
+#include "test_macros.h"
+
+template <typename T, typename SIZE_TYPE = std::size_t, typename DIFF_TYPE = std::ptrdiff_t>
+class sized_allocator {
+  template <typename U, typename Sz, typename Diff>
+  friend class sized_allocator;
+
+public:
+  using value_type                  = T;
+  using size_type                   = SIZE_TYPE;
+  using difference_type             = DIFF_TYPE;
+  using propagate_on_container_swap = std::true_type;
+
+  TEST_CONSTEXPR_CXX20 explicit sized_allocator(int d = 0) : data_(d) {}
+
+  template <typename U, typename Sz, typename Diff>
+  TEST_CONSTEXPR_CXX20 sized_allocator(const sized_allocator<U, Sz, Diff>& a) TEST_NOEXCEPT : data_(a.data_) {}
+
+  TEST_CONSTEXPR_CXX20 T* allocate(size_type n) {
+    if (n > max_size())
+      TEST_THROW(std::bad_array_new_length());
+    return std::allocator<T>().allocate(n);
+  }
+
+  TEST_CONSTEXPR_CXX20 void deallocate(T* p, size_type n) TEST_NOEXCEPT { std::allocator<T>().deallocate(p, n); }
+
+  TEST_CONSTEXPR size_type max_size() const TEST_NOEXCEPT {
+    return std::numeric_limits<size_type>::max() / sizeof(value_type);
+  }
+
+private:
+  int data_;
+
+  TEST_CONSTEXPR friend bool operator==(const sized_allocator& a, const sized_allocator& b) {
+    return a.data_ == b.data_;
+  }
+  TEST_CONSTEXPR friend bool operator!=(const sized_allocator& a, const sized_allocator& b) {
+    return a.data_ != b.data_;
+  }
+};
+
+#endif
----------------
ldionne wrote:

```suggestion
#endif // TEST_SUPPORT_SIZED_ALLOCATOR_H
```

https://github.com/llvm/llvm-project/pull/122410